Method and apparatus for detecting gas in well drilling fluids



Feb 8, 1944, R. wfwlLsoN ET AL 2,341,169

METHOD AND APPARATUS FOR DETECTTNG GAS IN WELL DRILLING FLUIDS FiledDec:y 50, 1940 if Jdcklall? Ml'dleda Plz INVENTORS BY f7 HOM ATTORNEYPatented Feb. 9 lgdd lit ME'I'HD APPARTUS FR DETIEUHNG GAS IIN WELL DHNGFUUHDS Ralph W. Wilson, Houston,

Wichita Falls, Tex.,

Illulsal Okla., asslgno and Alfred Lona', Jr.,

and Martin '.l. Randolph, rs to National Lead Comd Claims.

This invention relates to methods and apparatus for the detection of gasin well drilling muds during the drilling of wells by the rotary method,wherein a stream of mud-laden drilling fluid is circulated through theWell during the drilling operations, whereby the gas-bearing formationsfrom which said gas came may be located.

In accordance with conventional rotary drilling practice, particularlyas practiced in the method embodying this invention, a mud duid,consisting generally of a suspension of clay solids in water, iscirculated through the well during the drilling thereof for the purposeof washing drill cuttings from the well, plastering the wall of the wellbore, keeping the bit clean, etc. rdinarily, the specific gravity of thedrilling uid is so controlled, as by adding high specific gravityweighting materials thereto, such as barytes, iron oxide, etc., that thehydrostatic head of the drilling fluid column is maintainedsubstantially in excess of the pressures of any of the cognate uids,such as gas, oil, and water, contained in. any of the formationstraversed by the drill. Also, a gel-component, such as colloidal claylike bentonite, is added to the mud fluid to maintain the solidcomponents of the mud fluid, that is, the clay and weighting materials,in v:more or less permanent suspension. and to aid in quickly sealing upand plastering the formations traversed by the drill. The resultingdrilling fluid is generally a viscous fluid of about the consistency ofheavy lubricating cil. As a result of the excess head of the column ofdrilling uid and of its wall sealing and plastering properties.

when a uid bearing formation, such as a gasbearing stratum, is piercedby the drill, the excess head of the drilling fluid column and itssealing properties will act promptly to prevent the inflow of the gasinto the well bore and into the column of mud fluid, and to eectivelyseal up such stratum. In fact, in modern rotary drilling practice, greatcare is exercised in carefully controlling the properties of the mudfluid vsoA that no such inflows will occur, since otherwise. there isgreat danger that the high pressure cognate fluids will enter the wellbore in sufficient quantities to cause disastrous blow-outs, withconsequent great hazard to the well and to life and property in thevicinity of the well.

Hayward Patent No. 2,214,674, dated September 10, 1940, disclosed thatunder the above-described conditions oi modern rotary drilling practice,wherein the inflow of cognate fluids from the traversed formations isprevented, certain exceedingly minute amounts of the cognate fluids willbe present in the circulating uid, and that such minute amounts of thecognate fluids can be detected in the drilling duid returns leavz ingthe well, and that the location of the fluidbearing strata responsibletherefor can be determined by suitable methods disclosed in that patentfor tracing the flow of successive increments of the mud fluid throughthe well and identifying the emerging increments with the correspondingstrata responsible for the presence of the cognate fluids in therespective increments.

These minute quantities of the cognate fluids, such as gas, present inthe mud nuid, are those very small quantities contained in thecylindrical core of the fluid-bearing strata which is continuously cutfrom the strata, ground up by the blt, and dispersed in the stream ofmud fluid continuously flowing past the bit, as distinguished from thefluids flowing into the well from the surrounding strata. The smallquantities of gas thusintroduced into the drilling fluid will becomewidely dispersed therein in the form of relatively minute globules, oras thin lms on the surfaces of the particlescf solid matter contained inthe drilling iluid, or in solution to some extent in the aqueous phaseof the drilling fluid, and an effective method of separation anddetection of these minute amounts of gas becomes very necessary to aidin accurately locating the gas-bearing formations.

'I'he present invention employs the basic concepts of the Haywardinvention for correlating the successive portions of the drilling fluidreturns with the sub-surface strata, but is directed particularly to animproved method and apparatus for separating and' detecting the minuteamounts of gas in the drilling fluids during drilling and fordetermining the location o the strata responsible therefor.

Generally stated and in accordance with the illustrative embodiments ofthis invention, the ilow of drilling fluid is suitably traced throughthe well in order to correlate each portion of the emerging fluid withthe corresponding subsurface strata; a minor portion of the emergingfluid is continuously diverted from the main stream thereof and causedto flow through a separating zone in intimate contact with an introducedstream of air whereby any minute amounts of gas which may be occluded inthe drilling fluid are caused to separate from the drilling fluid; a.constant volume of the separated gaseous fluid is withdrawn from theseparating zone substantiatly as rapidly as it is evolved from thedrilling fluid, and. is continuously analyzed for gas, to thereby detectthe presence of gas in the drilling fluid and the amount thereof. Wateror a suitable chemical gas-releasing agent may be added to the divertedportion of the drilling fluid stream to assist the contacting air ineffecting release of any occluded gas from the drilling uld.

The step of subjecting only a minor portion of the drilling uid streamto analysis for gas is particularly useful, for very often the gas willbe tightly occluded in the mud uid because o its viscosity, or by reasonof the gel-component therein or will be in the fluid in the form of anemulsion, or in solution, and it becomes necessary to dilute the mudwith water or treat it with viscosity-reducing or emulsion-breakingchemicals to eiect release of suillcient gas for analysis. To so treatthe entire stream of mud iluld would ordinarily be both prohibitive incost, and in many cases highly detrimental to the mud fluid, sincetreatment would often destroy the necessary gel-component of the mud Iand thereby render the entire body of the mud fluid practicallyvalueless and ineffective for further drilling. By the improved methodand apparatus contemplated by this invention, such an undesirable resultis avoided and separation and detection of the gas and location of thegas bearing strata is effectively accomplished.

The various objects and advantages of this novel invention will be morereadily understood from the following detailed description, when read incommotion with the accompanying drawing, which illustrates, more or lessdiagrammatically, apparatus suitable for practicing the improved methodsof this invention. It will be understood, however, that this inventionis not limited to any particular apparatus or mere details of steps, butthat various changes may be made in details but within the scope of theappended claims, without departing from the spirit of this invention.

In the drawing:

Fig. 1 illustrates an arrangement of apparatus in accordance with onemodification of this invention suitable for the practice thereof, and

Fig. 2 illustrates in greater detail a portion of the apparatusillustrated generally in Fig. 1.

Referring to the drawing and to Fig. l in particular, the numeral 2designates the upper end of the usual surface casing lining a well borebeing drilled in accordance with modern conventional rotary drillingmethods, by the employment of a circulating hydraulic fluid, such as asuspension of clay solids in water, generally of the composition asabove described, and conventionally termed rotary mud, drilling fluid ormud-laden uid. The upper end of casing 2 is provided with a side outletpipe 3 which discharges into the usual mud settling pit 4 where thesolid cuttings brought to the surface from the bottom of the well by thedrilling fluid are settled out. The settled mud iiuid flows through anover-now ditch'5 to a suction pit 6 from which the cuttings free mudfluid is withdrawn for return to the well. Extending into the well borethrough casing 2 is a conventional hollow drilling string, designatedgenerally vby the numeral 1, and having at its lower end the usual drillbit (not shown). A conventional Kelly joint 8 forms the upper end of thedrilling string and extends through a rotary table 9 conventionallymounted on the floor of derricl: l0. Ro-

tation of rotary table 9 rotates Kelly Joint l in the usual way to causerotation of the drilling string and of the blt to produce drilling ofthe strata encountered. The upper end of Kelly 5 Joint 8 is connected tothe usual rotary hose swivel II, and the entire drilling string -issuspended in the usual manner from a travelling block I2 which isadapted to be raised and lowered in thederrick by means of cables I3,all in accordance with common rotary drilling practice.

A mud pump I4 has its suction pipe I5, which leads to suction pit 6, anda discharge pipe I8 which communicates with the bore of the hollowdrilling string 1 through swivel II. A iluid meter I1 is positioned inpipe I6 and is adapted to measure the volumetric iiow of the mud uidpumped from suction pit 6 by pump I4 through pipes I5 and I6 to thedrilling string. Fluid meter I1 may be of any conventional type adaptedto measure units of drilling fluid passing through the well.

The depth of the well may be measured at all times by any conventionalmethod and this is commonly done by adding together the measurements ofthe lengths of all joints of drill pipe in the well, and by suitablymarking the Kelly joint to determine how much of its length hasdescended into the well. However, the depth measurements may beconveniently obtained by suitable mechanical or automatic measuringdevices such as that described in Hayward Patent No. 2,166,212, dated'July 18, 1939. A suitable mechanical depth measuring device isdiagrammatically represented in the drawing by a depth meter I8 operatedby means of a measuring line I9 passing over a measuring pulley 23 andleading over pulleys 2I and 22 to the traveling block I2, themeasurement of the depth of the well or the length of drill pipe in thewell being obtained thereby from the downward movements of the travelingblock as it follows the downward movements of the drilling string in thewell.

A branch pipe 23, having a valve 24, is oonnected into side outlet pipe3 and leads to the bottom of a hollow mixing chamber 25, into the upperend of which is connected a pipe 26, having a valve 21 interposedtherein. From the side of mixing chamber 25 a conduit 28 leads into theupper portion of a vertically positioned, elon- .gated separatingchamber 29, tted internally with a plurality of vertically spaced,downwardly sloping baille plates 30 (Fig. 2) From the lower end ofseparating chamber 29 a discharge pipe 3|, in which is mounted a valve32, leads over the mouth of settling pit 4. An air inlet pipe 83communicates with the interior of separating chamber 29 at a point aboveand adjacent to discharge pipe 3l. An outlet pipe 34, fitted with avalve 35, is in communication with the upper portion of separatingchamber 29 above the point of connection thereto of conduit 28, andconnects to a suction tube 36 which leads to a suitable gas detectionandv analysis apparatus, designated generally in Fig. 1 by the numeral31. Fig. 2 illustrates the gas detection and analysis apparatus insomewhat greater detail. Suction tube 36 leads to the lower inlet end ofa ilow meter 38 which may be of any suitable or conventionalconstruction. A convenient form of flow meter is illustrated in Fig.Zand is a commercial type known as the Rotameter," manufactured byFischer and Porter, Philadelphia, Pa., and is found to be well adaptedfor 75 use in this apparatus, for measuring the volume of gaseous iiuidwithdrawn from separating chamber 29. A pipe 39, in which is mounted aregulating valve 40, leads from the upper outlet end of ilow meter 38 tothe suction of a compressor di from the discharge of which a pipe t2leads to a gas analyzer 43, which is preferably of the conventionalelectric hot filament type commonly employed for analyzing air-gasmixtures for the presence and amount of combustible gases such as thehydrocarbon gases commonly encountered in drilling oil or gas wells.Analyzer d3 is provided with the usual register dil for indicating thepercentage of gas in the mixture passing through the analyzer, which isalso provided with a discharge pipe t5 for venting the products ofanalysis from the instrument. A valved branch pipe 46 is connected intopipe i2 at a point between compressor di and analyzer d3.

Detection of gas and location of the gas-bearing formation duringdrilling of an oil or gas well is accomplished by means of the abovedescribed apparatus in the following manner:

Rotary drilling is conducted in the conventional manner, whereby thedrilling string 'i is rotated to produce the cutting action of the drillbit at the bottom of the well, and a stream of drilling fluid, of thecharacter described above,

having a specific gravity such as to provide a.,

duid column pressure in the well in excess of the head in any stratumencountered by the drill and containing a `gel-component, is circulatedthrough the well. The drilling fluid is drawn from suction pit 6 throughpipe l5 by pump ifi and is discharged through pipe i5 and swivel il intothe interior of the drilling string. Upon reaching the bit at the bottomof the well, the mud is discharged through the usual openings. in thebit adjacent the bottom of the well into the annular space between thedrilling string and the wall of the well bore. As the fluid isdischarged into the annular space, the bit disperses therein theground-up particles of the segment of the stratum which the bit iscurrently cutting, together with any cognate iluids, such as gas or oil,present in the stratum. The drilling fluid containing the dispersedmaterials then ilows upwardly through the annular space to the top ofthe well where it is discharged through side outlet pipe 3 and flowstoward settling pit t. The ilow of the drilling iluid through the wellis continuously followed and each increment of the emerging fluid isrelated to the stratum corresponding thereto, that is, to the stratumresponsible for any cognate fluid which might be present in thatincrement, by cooperatively employing iluid meter il and depth meter i8in order to measure the depth of the well in synchronism with the riseof each increment of the drilling nuid to the top of the well in themanner disclosed in Hayward Patent No. 2,214,674, referred to above. Inthis way each increment of the drilling fluid iiowing through pipe 3towards settling pit 4'is continuously identied with the depth .positionof the corresponding stratum. I

As the drilling uid ows through pipe 3, a minor portion of the fluid iscontinuously diverted from the main stream in pipe 3 into pipe 23 byopening valve 24. The minor portion, which is ordinarily about onepercent of the total iluid, but may be more or less, then flows throughmixing chamber 25, where. if found necessary. a gas-releasing treatingagent. such as water. viscosity-reducing or emulsion-breaking chemicalsof a character well known to those skilled in this art. may be added tothe minor portion ot the drilling fluid by introduction through pipe 26under control of valve 2l, by which the quantity of treating agent soadded may be regulated. The drilling fluid, or mixture of drilling iluidand treating agents, then liows through conduit 2d into the upperportion of separating chamber 2t. Therein the drilling nuid ilowsdownwardly in a tortuous path over baille plates il to the lower portionof the separating chamber from which it eventually ilows, generally bygravity, through pipe 3i and valve 32 into settling pit t where it isremixed with the main stream of the drilling uid discharging from pipe3. Since the side stream of drilling iiuid sent through separator 2g isonly about one percent of thetotal volume of drilling uid it cannot haveany undesirable eiiect upon the entire body of drilling fluid whenre-mixed therewith even though the side stream contains some treatingagents. This is particularly true since the amount of treating agentwhich is normally added will often be less than one percent of theamount of the side stream. A slight suction is maintained in separatingchamber 29 by means of the suction of compressor di and this acts todraw air into the separating chamber through pipe 33 which is open tothe atmosphere. The entering air iiows upwardly through the separatingchamber in intimate counter-current contact with the down-flowing streamof drilling fluid and the intimate contact of the air with thedown-owing drilling fluid aerates the fluid and expels any gas which hasbeen occluded in the fluid. In some cases, only aeration in the mannerdescribed is necessary to eiect release of the gas from the drillingfluid, while in other cases, the combination of aeration and treatmentwith one or more of the abovementioned treating'agents will accomplishthis result. By manipulation of valve i0 in pipe 39. the suction appliedto separating chamber 29 through flow meter 3@ is such as to cause thecompressor 4l, cooperating with ow meter 3d, to withdraw a constantvolume of the gaseous fluid, comprising the mixture of gas and air, fromseparating chamber 29, and the withdrawn mixture is metered by iiowmeter 38. The volume of gaseous fluid so withdrawn is ordinarilyadjusted to such as will cause removal of the gas from chamber 29substantially as rapidly as it is evolved from each increment of thedrilling fluid entering the chamber. Since the volume or air-gas mixturewithdrawn is constant, then, as the volume of gas evolving from thedrilling fluid changes, the volume of air in the mixture withdrawn willchange proportionally, since the pressure conditions in chamber 29 areheld constant. The withdrawn air-gas mixture is then discharged bycompressor iii through pipe i2 and the detector-analyzer li3 whichindicates on register lill the percentage of gas in the mixture.Register M will thus continuously indicate the rate of evolution of gasfrom the drilling uid. Of course, when no gas is present in the drillingfluid, no indication will appear on register tt and the absence of gaswill thus be indicated. The indication on register 44 of any proportionof gas in the mixture serves to detect the presence of gas in thedrilling fluid and the changing percentages indicate the rate ofevolution of gas from the drilling fluid. Since, as noted, eachincrement of the drilling fluid entering separating chamber 29 hasalready been identied with its corresponding source stratum, theanalysis of the air-gas mixture will determine when a gasbearingformation has been penetrated, and to gether with the correspondingdepth data, will serve to locate the depth position of such formations.It will be understood, of course, that the air introduced intoseparating chamber 29 should be gas-free at all times.

Under the conditions of modern drilling, as set forth herein, where thefluid column pressure is at all times maintained in excess of theformation pressures, and since, ordinarily, from about 50 to 150 or morebarrels of drilling fluid are circulated through the well per foot offormation drilled, the volume of gas carried by any increment of thedrilling fluid will necessarily be quite small, often as little as 0.001cubic foot per minute being evolved from the uid. To make certain thatthe evolving gas is transported to the analyzer substantially as rapidlyas it evolves from the drilling uid, so that the analysis of eachportion of the gas may be accurately related to its correspondingincrement of the drilling fluid, the total volume of gaseous uidwithdrawn from separating chamber 29 is so regulated by adjustment ofvalve 40 that the volume of air entering the chamber will be sumcient tocontinuously purge the chamber and to carry the evolving gas directly tothe analyzer Without substantial lag or delay between the evolution andthe analysis. As an example, twenty cubic feet per minute of the air-gasmixture has been found to be a convenient volume to be continuouslywithdrawn from separator 29. The volume thus withdrawn will vary, ofcourse, with the size of separating chamber, the volume of gasordinarily evolved and other factors which will be apparent to thoseskilled in thisA art. It will also be understood that the entire volumeof the air-gas -mixture withdrawn from separating chamber 29 is notpassed through the analyzer 43, since such analyzers are generallyoperative only on small volumes. The bulk of the air-gas mixture is,therefore, generally by-passed around the analyzer through valved pipe46, and only enough for purposes of analysis is sent to the analyzerthrough pipe 42.

What we claim and desire to secure by Letters Patent is:

l. The method of detecting gas in drilling mud returns from a Wellduring drilling, comprising, flowing drilling mud returns from the wellthrough a separating chamber, introducing a counter-current of air intosaid separating chamber into intimate contact with said drilling mud,withdrawing the resulting gaseous fluid from said separating chamber,and analyzing said fluid for gas.

2. The method of detecting gas in the drilling mud returns from a wellduring drilling, comprising, flowing the drilling mud returns from thewell, 'diverting a minor portion of the returns from the main streamthereof, flowing said minor portion through a separating chamber,

introducing a counter-current of air into said separating chamber intointimate contact with said minor portion of the drilling mud-returns.withdrawing the resulting gaseous iluid from said separating chamber,and analyzing the fluid for gas.

3. The method of detecting gas which has become dilutedly occluded inthe circulating drilling fluid employed in the drilling of an oil or gaswell by the drilling of a stratum while the nuld column is maintained ata head exceeding the head of the stratum, comprising, flowing drillingfluid returns from the top of the well into intimate contact with acounter-current of air to thereby eifect release of occluded gastherefrom,

separating the resulting air-gas mixture from' said iiuid, and analyzingsaid mixture for gas.

4. Apparatus for detecting gas in the drilling fluid returns from a wellduring drilling, comprising, in combination with a discharge pipe for'discharging drilling fluid returns from the top of a well, a mixingchamber, a branch pipe connecting said discharge pipe to said mixingchamber, a second pipe connected to said mixing chamber, a separator, aconduit connecting said mixing chamber to said separator, an air inletpipe for said separator, liquid-gas contacting means in said separatorinterposed between said conduit and said air inlet pipe, a. liquiddischarge pipe from said separator, a suction pipe connected to saidseparator, a flow meter interposed in said suction pipe, a gas analyzerconnected to said suction pipe, and a compressor operatively associatedwith said suction pipe for producing a now of gaseous fluid through saidsuction pipe from said separator and through said flow meter and saidgas analyzer.

5. The method of detecting gas in the drilling mud returns from a wellduring drilling, comprising, flowing the drilling mud returns from thewell, after admixture therewith of a viscosity-reducing agent, through aseparating chamber, introducing a counter-current of air into saidseparating chamber into intimate contact with said drilling mud,withdrawing the resulting gaseous fluid from said separating chamber andanalyzing the gaseous fluid for gas.

6. The method of detecting gas in the drilling mud returns from a wellduring drilling, comprising, flowing the drilling mud returns from thewell through a separating chamber, introducing a counter-current of airinto said separating chamber into intimate contact with said drillingmud, maintaining constant suction in said separating chamber to therebyWithdraw from said separating chamber a constant volume of said gaseousfluid substantially as rapidly as it evolves from said drilling fluid,and analyzing the withdrawn gaseous iluid for gas.

RALPH W. WILSON. ALFRED LONG, JR. MARTIN T. RANDOLPH.

